1. Field of the Invention
The present invention generally relates to a communication system. More particularly, the present invention relates to an apparatus and method for receiving a signal in a communication system.
2. Description of the Related Art
In general, communication systems are being developed to provide high-speed, large-data transmission services to Mobile Stations (MSs). In this context, Low Density Parity Check (LDPC) codes are seriously considered for the communication systems, because the LDPC codes are channel codes suitable for high-speed, large-data transmission.
With reference to FIG. 1, the configuration of a signal transmission apparatus in a conventional communication system using LDPC codes will be described below.
Referring to FIG. 1, the signal transmission apparatus includes an encoder 111, a modulator 113, and a transmitter 115. Upon generating transmission data, i.e. an information vector, the encoder 111 encodes the information vector to a codeword vector in a predetermined coding scheme. Herein, the coding scheme is an LDPC coding scheme, and thus the codeword vector is an LDPC codeword. The modulator 113 modulates the LDPC codeword in a predetermined modulation scheme. The transmitter 115 processes the modulated vector received from the modulator 113 and transmits the processed signal to a signal reception apparatus through an ANTenna (ANT).
With reference to FIG. 2, a configuration of a signal reception apparatus in a conventional communication system using LDPC codes will be described below.
Referring to FIG. 2, the signal reception apparatus includes a receiver 211, a demodulator 213, and a decoder 215. The receiver 211 processes a signal received from the signal transmission apparatus through an ANTenna (ANT). The demodulator 213 demodulates the received vector received from the receiver 211 in a demodulation scheme corresponding to the modulation scheme of the modulator 113. The decoder 215 decodes the demodulated vector received from the demodulator 213 in a decoding scheme corresponding to the coding scheme of the encoder 111 and outputs the decoded signal as a final recovered information vector. It is assumed herein that the decoding scheme, i.e. the LDPC decoding scheme, is performed by a sum-product iterative decoding algorithm.
An LDPC code is defined by a parity check matrix that mostly contains zeroes, and a very small number of non-zeroes, for example, ones. The LDPC code can be represented as a bipartite graph. The bipartite graph includes variable nodes (i.e. bit nodes), check nodes, and edges connecting the variable nodes and the check nodes.
A sum-product iterative decoding algorithm on the bipartite graph can decode the LDPC code. The sum-product algorithm is a type of message passing algorithm that exchanges messages along edges, calculates outgoing messages from incoming messages to the bit nodes or check nodes, and updates the nodes on the bipartite graph.
In implementing the message-passing algorithm on the bipartite graph, a bit node operation and a check node operation are sequentially performed, i.e., the bit node operation is sequentially performed on all bit nodes, and the check node operation is sequentially performed on all check nodes. As stated before, due to the nature of iterations of the LDPC decoding, the resulting increase in the time for detecting a final decoding result leads to an increase in an LDPC decoding time delay. Accordingly, there exists a need for reducing the time taken for LDPC decoding without affecting LDPC decoding performance.